The present invention relates to an antiskid control system.
In conventional antiskid control systems, the down pressure timing of hydraulically operated brakes is determined by a first down pressure decision threshold with which detected wheel speed values are compared and by a second down pressure decision threshold with which wheel acceleration values are compared to determine the optimum slip rate of the wheels. With antiskid control systems of this type, the threshold values are determined by the vehicle speed which is from the maximum wheel speed value. However, differences in wheel diameter between wheels may cause a down-pressure operation to occur at false timing. More specifically, if a given wheel has a lower tire pressure than the other wheels, the diameter of the given wheel is smaller than the others and its apparent wheel speed is greater than the speed of any other wheel. This apparent wheel speed is then taken as a maximum speed. Thus, the estimated vehicle speed value is higher than is required for optimum operation of the brakes of the other wheels. Such situations may also occur in a vehicle running on a curved path. On a right-turn curve, for example, the front right wheel would turn at speeds lower than the front left wheel, so that the front right wheel speed Vwr becomes smaller than the front left wheel speed Vwl. At time Ta this reduces below down pressure decision threshold Vs, as shown in FIG. 1. Pressure down operation thus occurs prematurely and the fluid pressure on a vehicle wheel following a smaller radius reduces excessively in comparison with the fluid pressure on the wheel on the other side of the axle.